In situ SEM micro-indentation of single wood pulp fibres in transverse direction.

Fibre deformations such as kinks and micro-compressions are significant parameters in determining the quality of industrial pulps. Undoubtedly, very little information has been obtained so far on fibre deformation because it is very tedious to handle the specimens. In this study, a novel in situ scanning electron microscope (SEM) micro-indentation technique was adopted for the first time to study the deformation of single industrial pulp fibres in the transverse direction. A one-to-one correspondence between load drops in load-displacement curve and cell wall deformation was obtained by using the SEM video sequence recorded during micro-indentation. The cell wall deformation occurred by 'elastic' sinking-in and lateral bulging of the microfibrils. Finally, the critical load (stress) required to initiate a crack in the cell wall was measured for different unbleached pulp fibres.

In situ SEM indentation experiments: instruments, methodology, and applications.

The purpose of this article is to present the design and capabilities of two in situ scanning electron microscope (SEM) indentation instruments covering a large load range from microN to N. The capabilities and advantages of in situ SEM indentation are illustrated by two applications: indentation of a thin film and a nanowire. All the experiments were performed on electrodeposited cobalt, whose outstanding magnetic properties make it a candidate material for MEMS and NEMS devices.

Hydrothermal and mechanical stresses degrade fiber-matrix interfacial bond strength in dental fiber-reinforced composites.

Fiber-reinforced composites (FRCs) show great promise as long-term restorative materials in dentistry and medicine. Recent evidence indicates that these materials degrade in vivo, but the mechanisms are unclear. The objective of this study was to investigate mechanisms of deterioration of glass fiber-polymer matrix bond strengths in dental fiber-reinforced composites during hydrothermal and mechanical aging. Conventional three-point bending tests on dental FRCs were used to assess flexural strengths and moduli. Micro push-out tests were used to measure glass fiber-polymer matrix bond strengths, and nanoindentation tests were used to determine the modulus of elasticity of fiber and polymer matrix phases separately. Bar-shaped specimens of FRCs (EverStick, StickTech, and Vectris Pontic, Ivoclar-Vivadent) were either stored at room temperature, in water (37 and 100 degrees C) or subjected to ageing (10(6) cycles, load: 49 N), then tested by three-point bending. Thin slices were prepared for micro push-out and nanoindentation tests. The ultimate flexural strengths of both FRCs were significantly reduced after aging (p < 0.05). Both water storage and mechanical loading reduced the interfacial bond strengths of glass fibers to polymer matrices. Nanoindentation tests revealed a slight reduction in the elastic modulus of the EverStick and Vectris Pontic polymer matrix after water storage. Mechanical properties of FRC materials degrade primarily by a loss of interfacial bond strength between the glass and resin phases. This degradation is detectable by micro push-out and nanoindentation methods.